Tuesday, 09 May, 2017

Semiconductors as decal stickers

Organic electronics

Put an end to error-prone evaporation deposition, drop casting or printing: Scientists from LMU Munich and FSU Jena have developed organic semiconductor nanosheets which they can easily remove from a perfect growth substrate and place onto other preferred substrates.

Today’s computer processors are composed of billions of transistors. These electronic components normally consist of semiconductor material, insulator, substrate, and electrode. A dream of many scientists is to have each of these elements available as transferable sheets, which would allow them to design new electronic devices simply by stacking.

This has now become a reality for the organic semiconductor material pentacene: Dr. Bert Nickel (NIM, LMU Munich) and Professor Andrey Turchanin (Friedrich Schiller University Jena) together with their teams managed to create mechanically stable pentacene nanosheets, a first-time success.

Transport by tweezers

The scientists describe their method in the journal Advanced Materials; they cover a small silicon wafer with a thin layer of a water-soluble organic film and deposit pentacene molecules until a roughly 50 nanometer thin layer is formed. The next step is crucial: by irradiation with low-energy electrons, the topmost three to four levels of pentacene molecular layers are crosslinked forming a “skin”, which is only about five nanometers thin. This crosslinked layer stabilizes the entire pentacene film so well that it can be removed from a silicon wafer in water as a sheet and transported to another surface by using common tweezers.

Hardly any resistance

Apart from the ability to transfer, the new semiconductor nanosheets have other advantages as well; the new method does not require any disturbing solvents, for example. In addition, after deposition the nanosheet sticks firmly to the electrical contacts just by van der Waals forces resulting in a low contact resistance of the final electronic devices. Last but not least now organic semiconductor nanosheets can be deposited onto significantly more technologically relevant substrates than it has been possible so far.

Potential applications

Of particular interest is an extremely high mechanical stability of the newly developed pentacene nanosheets enabling their spanning as free-standing nanomembranes over millimeter-sized holy substrates. That is as if you would span a 25-meter pool with a plastic wrap. “These virtually freely suspended semiconductors have great potential,” explains Nickel. “They can be accessed from two sides and could be connected through an electrolyte, which would make them an ideal biosensor, for example”. “Another promising application is their implementation in flexible electronics for manufacturing of devices for vital data acquisition or production of displays and solar cells” Turchanin says.